Conventionally, there has been known a water pump for an automobile in which a mechanical seal is attached for sealing an annular gap between a housing and a shaft. Attaching a mechanical seal in this manner separates inside of the housing into a sealed-fluid side (pump chamber) where fluid to be sealed is sealed, and an atmosphere side (bearing chamber).
In the recent years, due to an increase in the optimal operation temperature range for the purpose of improving the thermal efficiency of an engine, reduction in size of the water pump and increase in the rotational speed of the water pump for the purpose of achieving high performance, there is a trend of increasing the pressure of the sealed-fluid side (pump chamber).
The increase in the pressure of the sealed-fluid side creates a difference in pressure balance between a rotating side and a stationary side of the mechanical seal, causing a cup gasket for sealing an annular gap between a sleeve and a mating ring (rotating ring) at the rotating side to move in the axial direction. Such movement of the cup gasket may make the sealing performance unstable.